Re: dropdb --force

čt 7. 11. 2019 v 6:56 odesílatel Amit Kapila <amit.kapila16@gmail.com>
napsal:

> On Thu, Nov 7, 2019 at 10:46 AM Pavel Stehule <pavel.stehule@gmail.com>
> wrote:
> >
> > čt 7. 11. 2019 v 3:42 odesílatel Amit Kapila <amit.kapila16@gmail.com>
> napsal:
> >>
> >> On Wed, Nov 6, 2019 at 11:46 PM Pavel Stehule <pavel.stehule@gmail.com>
> wrote:
> >> >
> >> > st 6. 11. 2019 v 14:59 odesílatel Tom Lane <tgl@sss.pgh.pa.us>
> napsal:
> >> >>
> >> >> Amit Kapila <amit.kapila16@gmail.com> writes:
> >> >> > I think there is still a window where the same problem can happen,
> say
> >> >> > the signal has been sent by SendProcSignal to the required process
> and
> >> >> > it releases the ProcArrayLock.  Now, the target process exits and a
> >> >> > new process gets the same pid before the signal is received.
> >> >>
> >> >> In principle, no use of Unix signals is ever safe against this sort
> >> >> of race condition --- process A can never know that process B didn't
> >> >> exit immediately before A does kill(B, n).  In practice, it's okay
> >> >> because the kernel is expected not to reassign a dead PID for some
> >> >> reasonable grace period [1].  I'd be inclined to lean more heavily
> >> >> on that expectation than anything internal to Postgres.  That is,
> >> >> remembering the PID we want to kill for some small number of
> >> >> microseconds is probably a safer API than anything that depends on
> >> >> the contents of the ProcArray, because there indeed *isn't* any
> >> >> guarantee that a ProcArray entry won't be recycled immediately.
> >> >>
> >>
> >> Right, this makes sense.  I think I was overly paranoid about this
> >> behavior even though that was used at a few other places as this patch
> >> might need to rely on many pids not being reused after the lock is
> >> released.
> >>
> >> >
> >> >
> >> > so we can return back to just simple killing.
> >> >
> >>
> >> I think so.  I think we might want to add a comment about this race
> >> condition and add or reference to comments in pg_signal_backend which
> >> mentions the same race condition.
> >
> >
> > Please, can you do it. It's bad task for my with my bad English.
> >
>
> Okay, no problem.  I will pick the previous version and do this.  I
> will post the patch in a day or so for your review.
>

Thank you very much

Pavel

>
> --
> With Regards,
> Amit Kapila.
> EnterpriseDB: http://www.enterprisedb.com
>